1. Field of the invention
The invention relates to the therapeutic use of oligonucleotides or oligonucleotide analogs as immunostimulatory agents in immunotherapy applications.
2. Summary of the related art
Oligonucleotides have become indispensable tools in modern molecular biology, being used in a wide variety of techniques, ranging from diagnostic probing methods to PCR to antisense inhibition of gene expression and immunotherapy applications. This widespread use of oligonucleotides has led to an increasing demand for rapid, inexpensive and efficient methods for synthesizing oligonucleotides.
The synthesis of oligonucleotides for antisense and diagnostic applications can now be routinely accomplished. See e.g., Methods in Molecular Biology, Vol 20: Protocols for Oligonucleotides and Analogs pp. 165-189 (S. Agrawal, Ed., Humana Press, 1993); Oligonucleotides and Analogues: A Practical Approach, pp. 87-108 (F. Eckstein, Ed., 1991); and Uhlmann and Peyman, supra. Agrawal and Iyer, Curr. Op. in Biotech. 6: 12 (1995); and Antisense Research and Applications (Crooke and Lebleu, Eds., CRC Press, Boca Raton, 1993). Early synthetic approaches included phosphodiester and phosphotriester chemistries. Khorana et al., J. Molec. Biol. 72: 209 (1972) discloses phosphodiester chemistry for oligonucleotide synthesis. Reese, Tetrahedron Lett. 34: 3143-3179 (1978), discloses phosphotriester chemistry for synthesis of oligonucleotides and polynucleotides. These early approaches have largely given way to the more efficient phosphoramidite and H-phosphonate approaches to synthesis. Beaucage and Caruthers, Tetrahedron Lett. 22: 1859-1862 (1981), discloses the use of deoxynucleoside phosphoramidites in polynucleotide synthesis. Agrawal and Zamecnik, U.S. Pat. No. 5,149,798 (1992), discloses optimized synthesis of oligonucleotides by the H-phosphonate approach.
Both of these modern approaches have been used to synthesize oligonucleotides having a variety of modified internucleotide linkages. Agrawal and Goodchild, Tetrahedron Lett. 28: 3539-3542 (1987), teaches synthesis of oligonucleotide methylphosphonates using phosphoramidite chemistry. Connolly et al., Biochemistry 23: 3443 (1984), discloses synthesis of oligonucleotide phosphorothioates using phosphoramidite chemistry. Jager et al., Biochemistry 27: 7237 (1988), discloses synthesis of oligonucleotide phosphoramidates using phosphoramidite chemistry. Agrawal et al., Proc. Natl. Acad. Sci. USA 85: 7079-7083 (1988), discloses synthesis of oligonucleotide phosphoramidates and phosphorothioates using H-phosphonate chemistry.
More recently, several researchers have demonstrated the validity of the use of oligonucleotides as immunostimulatory agents in immunotherapy applications. The observation that phosphodiester and phosphorothioate oligonucleotides can induce immune stimulation has created interest in developing this side effect as a therapeutic tool. These efforts have focused on phosphorothioate oligonucleotides containing the dinucleotide CpG.
Kuramoto et al., Jpn. J. Cancer Res. 83: 1128-1131 (1992) teaches that phosphodiester oligonucleotides containing a palindrome that includes a CpG dinucleotide can induce interferon-alpha and gamma synthesis and enhance natural killer activity. Krieg et al., Nature 371: 546-549 (1995) discloses that phosphorothioate CpG-containing oligonucleotides are immunostimulatory. Liang et al., J. Clin. Invest. 98: 1119-1129 (1996) discloses that such oligonucleotides activate human B cells.
Pisetsky, D. S.; Rich C. F., Life Sci. 54: 101 (1994), teaches that the immunostimulatory activity of CpG-oligos is further enhanced by the presence of phosphorothioate (PS) backbone on these oligos. Tokunaga, T.; Yamamoto, T.; Yamamoto, S. Jap. J. Infect. Dis. 52: 1 (1999), teaches that immunostimulatory activity of CpG-oligos is dependent on the position of CpG-motif and the sequences flanking CpG-motif. The mechanism of activation of immune stimulation by CpG-oligos has not been well understood. Yamamoto, T.; Yamamoto, S.; Kataoka, T.; Tokunaga, T., Microbiol. Immunol. 38:831 (1994), however, suggests that CpG-oligos trigger immune cascade by binding to an intracellular receptor/protein, which is not characterized yet.
Several researchers have found that this ultimately triggers stress kinase pathways, activation of NF-KB and induction of various cytokines such as IL-6, IL-12, γ-IFN, and TNF-α. (See e.g., Klinman, D. M.; Yi, A. K.; Beaucage, S. L.; Conover, J.; Krieg, A. M., Proc. Natl. Acad. Sci. U.S.A. 93: 2879 (1996); Sparwasser, T.; Miethke, T.; Lipford, G. B.; Erdmann, A.; Haecker, H.; Heeg, K.; Wagner, H., Eur. J. Immunol. 27: 1671 (1997); Lipford, G. B.; Sparwasser, T.; Bauer, M.; Zimmermann, S.; Koch, E. S.; Heeg, K.; Wagner, H. Eur. J., Immunol. 27: 3420 (1997); Sparwasser, T.; Koch, E. S.; Vabulas, R. M.; Lipford, G. B.; Heeg, K.; Ellart, J. W.; Wagner, H., Eur. J. Immunol. 28: 2045 (1998); and Zhao, Q.; Temsamani, J.; Zhou, R. Z.; Agrawal, S. Antisense Nucleic Acid Drug Dev. 7:495 (1997).)
The use of CpG-PS-oligos as antitumor, antiviral, antibacterial and antiinflammatory agents and as adjuvants in immunotherapy has been reported. (See e.g., Dunford, P. J.; Mulqueen, M. J.; Agrawal, S. Antisense 97: Targeting the Molecular Basis of Disease, (Nature Biotechnology) Conference abstract, 1997, pp 40; Agrawal, S.; Kandimalla E. R. Mol. Med. Today 6:72 (2000); Chu. R. S.; Targoni, O. S.; Krieg, A. M.; Lehmann, P. V.; Harding, C. V. J. Exp. Med. 186: 1623 (1997); Zimmermann, S.; Egeter, O.; Hausmann, S.; Lipford, G. B.; Rocken, M.; Wagner, H.; Heeg, K. J. Immunol. 160: 3627 (1998).) Moldoveanu et al., Vaccine 16: 1216-124 (1998) teaches that CpG-containing phosphorothioate oligonucleotides enhance immune response against influenza virus. McCluskie and Davis, J. Immunol. 161: 4463-4466 (1998) teaches that CpG-containing oligonucleotides act as potent adjuvants, enhancing immune response against hepatitis B surface antigen.
Zhao, Q.; Temsamani, J.; Idarola, P.; Jiang, Z.; Agrawal, S. Biochem. Pharmacol. 51: 173 (1996), teaches that replacement of deoxynucleosides in a CpG-motif with 2′-O-methylribonucleosides suppresses immunostimulatory activity, suggesting that a rigid C3′-endo conformation induced by 2′-Omethyl modification does not allow proper recognition and/or interaction of CpG-motif with the proteins involved in the immunostimulatory pathway. This reference further teaches that substitution of a methyl group for an unbridged oxygen on the phosphate group between C and G of a CpG-motif suppresses immune stimulatory activity, suggesting that negative charge on phosphate group is essential for protein recognition and interaction.
Zhao, Q.; Yu,. D.; Agrawal, S. Bioorg. Med. Chem. Lett. 9: 3453 (1999), teaches that substitution of one or two 2′-deoxynucleosides adjacent to CpG-motif with 2′- or 3′-O-methylribonucleosides on the 5′-side causes a decrease in immunostimulatory activity, while the same substitutions have insignificant effect when they were placed on the 3′-side of the CpG-motif. However, Zhao, Q.; Yu, D.; Agrawal, S. Bioorg. Med. Chem. Lett. 10: 1051 (2000), teaches that the substitution of a deoxynucleoside two or three nucleosides away from the CpG-motif on the 5′-side with one or two 2′-O-methoxyethyl- or 2′- or 3′-O-methylribonucleosides results in a significant increase in immunostimulatory activity.
The precise structural requirements and specific functional groups of CpG-motif necessary for the recognition of protein/receptor factor that is responsible for immune stimulation have not yet been studied in detail. There is, therefore, a need for new immunostimulatory motifs which may provide improved immunostimulatory activity.